In a plasma processing apparatus for performing plasma processing for wafers such as semiconductor wafers (formed of Si, compounds or the like), the plasma processing such as etching on wafers is conducted with the wafers placed and held on a placement surface of a wafer holding device provided in a processing vessel. In such a wafer holding device, an electrostatic chuck, which is commonly referred to as “ESC,” is embedded in the placement surface, and the wafers are held with use of electrostatic attracting forces composed of Coulomb force and/or Johnson-Rahbeck force that are produced by the electrostatic chuck.
In such a conventional wafer holding device, electrostatic attracting forces that are effected by electric charge accumulated on the placement surface and the wafers remain (which forces will be referred to as “residual electrostatic attracting forces” below) even after the electrostatic attraction by the ESC is stopped, and thus various techniques have been proposed for releasing the wafers from the placement surface of the wafer holding device (see Patent Document 1, for instance).    Patent Document 1: JP 2005-217356 A    Patent Document 2: JP 2007-109770 A